The type of energy transformed into thermal energy in a toaster is electrical energy.

Here's how it works:

* Electrical Energy: When you plug the toaster into an outlet, electrical energy flows through the heating element inside.

* Resistance: The heating element is made of a material with high resistance, meaning it resists the flow of electricity. This resistance causes the element to heat up.

* Thermal Energy: The heated element transfers its heat to the bread, converting the electrical energy into thermal energy, which is what cooks the bread.